diff --git a/mrbgems/mruby-math/src/math.c b/mrbgems/mruby-math/src/math.c
index 39fed6cd3..ef0dc1857 100644
--- a/mrbgems/mruby-math/src/math.c
+++ b/mrbgems/mruby-math/src/math.c
@@ -120,6 +120,7 @@ erf(double x)
     term *= xsqr/j;
     sum  += term/(2*j+1);
     ++j;
+    if (sum == 0) break;
   } while (fabs(term/sum) > DBL_EPSILON);
   return two_sqrtpi*sum;
 }